<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <button id="btn">获取event对象</button>
<script>
  var btn = document.getElementById('btn');
  btn.onclick = function(e) {
    var event = e || window.event;  
    console.log(event);
  };
</script>
</head>
<body>
    
</body>
</html>